We propose to use the higher resolving power and high contrast of an advanced state-of-the art small focal spot "soft" (low kvp) x-ray unit to study microvascular changes in brains from hypertensive primates and humans and to compare the changes seen with normative controls. Patients with hypertension have a greatly increased incidence of intracerebral hemorrhage and cerebral infarcts. The light microscope has been used extensively to study the microvascular changes in this disease process, but analysis is limited by tissue thickness, i.e., only a small piece if the vascular bed can seen in any one section. Examination of a long, conplex anatomical unit such as an artery-capillary-venule complex is extremely tedious using thin section light microcscope in the evaluation of a longitudinal structure which is to be followed from one plane to the other. Because of the penetrating power and depth of focus, X ray is uniquely capable of examining the vascular bed. Human Material: Specimens of brain tissue from patients with hypertension will be studied for microcirculatory changes from hypertension and compared with normals. Small areas form five specific locations of already fixed brains in addition to spinal cord will be prepared by the histochemical technique originated by the coprincipal investigator and examined by x-ray microscopy. Then these same blocks of tissue will be cut and subjected to a detailed neutopthological examination. Animal Material: Specimens of fixed brain tissue form hypertensive primates will also be prepared, stained by the alkaline phophatase method devised by the coprincipal investigator and examined using both light and x-ray microscopy for microvascular changes and then compared with normals. We will move beyond previous microvascular studies in two areas: a) use of an advanced newly developed, nondestructive testing type x-ray unit that will increase resolving power; b) we will not use capricious barium perfusion angiographic techniques, but will stian the vascular tree directly using a recently developed histochemical staining technique devised by the co-principal investigator. It is believed that this study will identify the premorbid anatomical alteration leading to intracerbral hemorrhage or infarct in patients with hypetension.